Cotton is an important crop which is cultivated usually for fiber production. Fiber is collected from cotton bolls which are formed on cotton plant and have different application including textile and medical. Yield per plant is the most important attribute for the cotton growers besides fibre quality which leads to increasing acreage and market price. Yield of fiber in cotton plants depends on a number of internal and external characteristics (Harris, 2001. Cotton Farm. 45:26) including environmental, nutritional and hormonal conditions, expression of important proteins, as well as standard agricultural practices. Fiber yield is a combinatorial effect of fiber length, number of fibers per boll, and number of bolls per plant. Deviation in any of these parameters affects the yield of fiber in cotton (Haigler et al., 2005. Physiologia plantarum, 124(3), 285-294). Quality of cotton fiber is characterized by various factors including its length, fineness and strength.
Several approaches have been followed to improve the yield of cotton fiber on cotton plants (Lewis, 1992. The proceedings of cotton fiber cellulose: Structure function and utilization conference. p. 4-18. Savannah Ga. 28-31 Oct. 1992. Cotton Inc., Raleigh, N.C.) and these can be widely distributed in these classes on the basis of approach followed:
a. Breeding Approach
This is the most common approach for variety improvement. Conventional as well as marker based plant breeding approaches have been followed for fiber yield improvement in cotton (Meredith Jr, W R. 2005. Influence of cotton breeding on yield and fiber quality problems. Cotton Incorporated Proceedings. Jun. 6-8, 2005, Memphis, Tenn.). In India, H4 was the first cotton hybrids, which was released in 1970 and another hybrid Varalaxmi was released in 1972 (Singh et al., Breeding hybrid cotton, CICR technical bulletin No. 14, CICR, India).
Worldwide, several QTLs for yield and quality traits of cotton fiber have been identified and being used in breeding programme (Zhang et al., 2013. Variations and transmission of QTL alleles for yield and fiber qualities in Upland cotton cultivars developed in China. PloS one, 8(2), e57220; Jenkins et al., 2007. Genetic effects of thirteen Gossypizon barbadense L. chromosome substitution lines in toperosses with upland cotton cultivars: II. Fiber quality traits. Crop Science-Madison-47.2: 561). Although breeding approach in cotton has been a reliable method, the amount of time needed for development of an improved variety and limited variability available in cotton genotypes make this approach rather difficult.
b. Transgenic Approach
This includes variety improvement by gene recombination technique. Several attempts have been made to functionally characterize different genes and their introduction to the plants for expression/improvement of a desired trait thereon. Different genes encoding yield related proteins have been introduced to the cotton plants (Umbeck P F. Genetic engineering of cotton plants and lines, U.S. Pat. No. 5,004,863. 17 Oct. 2000). For example, method for increasing the quality of cotton fiber produced from a cotton plant by transformation with a DNA encoding sucrose phosphate synthase has been developed (Haigler & Holaday. 2002. U.S. Pat. No. 6,472,588. Washington, D.C.: U.S. Patent and Trademark Office). Similarly, expression of an Arabidopsis vacuolar H+-pyrophosphatase gene (AVP1) in cotton was also reported to increase fibre yield in the field conditions (Pasapula et al. 2011. Plant biotechnology journal 9.1 (2011): 88-99). Genes associated with fiber initiation and elongation has been incorporated for improving fiber characteristics and per plant yield in cotton (Pu et al. 2008. Genetics, 180.2, 811-820; and Lee et al., 2010. Planta 232.5, 11911205). But, as the fiber development in cotton is not fully elucidated and all the factors contributing fiber development and yield are not yet known, significant improvement in fiber yield has not been achieved by this approach.
c. Chemical Approach
This method majorly includes the application of plant hormones and growth supplements/stimulants directly on to the plant parts or in the soil. Plant hormones like auxin, gibberellin, cytokinin and ethylene are widely used to agricultural crops and horticultural products for alteration in different plant characteristics.
Several reports have been made citing the effect of these hormones on fiber quality and its yield. Auxin and gibberellin have been reported to promote fiber elongation by Bhardwaj and Sharma, 1971 (Ind J Agnc S ci. 41: 524-527), Singh and Singh, 1975 (Ind. J. Exp. Bioi. 13:411-412), Baert et al., 1975 (La Cellule, 71:55-63) and Gialvalis and Seagull, 2001 (The Journal of Cotton Science, 5:252-258). While, Dhindsa et al. (Planta (1976) 130:197-201) reported the inhibitory effect of abscisic acid on fiber elongation.
Similarly, brassinosteroids have been reported to promote fiber development in cotton ovule culture (Beasley and Ting, 1973. Amer J Bot, 60: 130-139; Sun et al., 2005. Plant and Cell Physiol. 46: 1384-1391). Gialvalis and Seagull, 2001 (The Journal of Cotton Science, 5:252258) confirmed that exogenous application of hormones for yield improvement in cotton is time dependent (pre or post anthesis). Acylsulfonamides are also reported to improve yield in cotton and other plants (Bayer Intellectual Property GMBH et al., Use of acylsulfonamides for improving plant yield. 20 Sep. 2013, U.S. Patent Application. PCT/EP2012/068096). Similarly, Abscisic acid (Nooden, Larry D. “Abscisic acid containing foliar fertilizers and method of using same to enhance crop yields”. U.S. Pat. No. 4,581,057. 8 Apr. 1986) and Imidazole (Cavender, Patricia L. “Imidazole plant growth regulators”. U.S. Pat. No. 4,565,875. 21 Jan. 1986) was also reported to enhance yield in cotton and other crop plants. Some commercial growth stimulants are also available in the market for crop plants.
Limitation in Prior Art
Although there are various growth stimulating formulations are available, their effect has not been consistent and fully confirmed to prove them effective for agricultural use. Some Phytohormones have also been used exogenously for plant yield improvement, but their effect is time dependent (Gialvalis and Seagull, 2001. The Journal of Cotton Science, 5:252258) and thus cannot be used as such for cotton plants, where flowering is largely asynchronous. Secondly, the quantity of the phytohormones needed for the effect is not well established. Hence there is a need for an effective formulation which can be used to increase yield and quality of cotton fiber and can be directly applied on the cotton plants. In the present invention this problem has been resolved.